1. Field of the Invention
The present invention relates to an input apparatus used in a SSTL interface, and more particularly to an input buffer circuit having a differential buffer and a CMOS buffer as input buffers, which enables the CMOS buffer to operate in a predetermined operation such as a refresh operation, thereby preventing a current consumption from the input buffers in a standby mode and reducing the current consumption.
2. Description of the Prior Art
The SSTL interface enables a potential of a signal inputted from an external to move above or below a predetermined reference potential (e.g. 1.4V) with a variation within a predetermined potential (e.g. 0.4V), instead of moving between a source potential and a ground potential.
A differential buffer circuit is mainly utilized as an input apparatus used in such a SSTL interface.
FIG. 1 is a circuit diagram of an input buffer in a conventional SSTL interface. An external input signal EXTIN represents an address signal, a control signal and a data signal, etc. As shown in FIG. 1, the input buffer is constructed by a differential comparison circuit 1 controlled by a control signal CTRL. The external input signal EXTIN is compared with a reference potential Vref, which is inputted from an external, to be outputted as an input signal INt2 of the SSTL interface. That is, two NMOS transistors N1 and N2 are respectively controlled by the external input signal EXTIN and the reference potential Vref. Further, by the control signal CTRL, two PMOS transistors P1/P4 and a NMOS transistor N3 function as a current source of the transistors N1 and N2 for the differential comparison. The input circuit as shown in FIG. 1 is called a differential input apparatus, and FIG. 1 shows other signals excepting a data signal from among the external input signals.
However, the conventional circuit as shown in FIG. 1 has a problem in that the circuit consumes a electric power even in a standby state.
That is, the buffers operate and consume electric power even in a predetermined time period for which the input apparatus does not operate. For instance, even though an external command signal is not inputted while a refresh operation is performed, these input apparatuses (command and address buffer) are turned on, thereby consuming a current.
Further, when the reference potential Vref varies, these input apparatuses do not normally operate. For instance, in the case of a standby mode in which a command signal is not inputted from an external in order to reduce a power consumption of a semiconductor apparatus, the reference potential Vref is floated. Herein, the reference potential Vref signal is changed into a ground potential, so that an abnormal operation may occur.